Metal-Oxide-Semiconductor (MOS) technology has been used widely. A MOS device can work in three regions including a linear region, a saturation region, and a sub-threshold region, depending on the gate voltage Vg and the source-drain voltage Vds. The sub-threshold region is a region where voltage Vg is smaller than the threshold voltage Vt. A parameter known as sub-threshold swing (SS) represents the easiness of switching the transistor current off, and is a factor in determining the speed of a MOS device. The sub-threshold swing can be expressed as a function of m*kT/q, where m is a parameter related to capacitance, k is the Boltzman constant, T is the absolute temperature, and q is the magnitude of the electrical charge on an electron. Previous studies have revealed that the sub-threshold swing of a typical MOS device has a limit of about 60 mV/decade at room temperature, which in turn sets a limit for further scaling of operational voltage VDD and threshold voltage Vt. This limitation is due to the diffusion transport mechanism of carriers. For this reason, existing MOS devices typically cannot switch faster than 60 mV/decade at room temperatures.